Apparatus for the measurement of the mechanical output of induction motors

Abstract

Apparatus for measuring and/or supervising the output power of an induction motor comprising means for generating a first voltage signal proportional to the synchronous speed of the motor, means for generating a second voltage signal proportional to the actual speed of the motor in operation and means responsive to the first and second voltage signals for generating a third voltage signal proportional to the difference between the first and second voltage signals. The third voltage signal is applied to a meter for providing a continuous indication of the output power of the motor.

I claim: 
     
       1. An apparatus for measuring and/or supervising the output of an induction motor comprising: means for generating a first voltage signal (S) corresponding to the synchronous speed of said motor;   means for generating a second voltage signal (H) proportional to the rotary speed of said motor at rated maximum output;   means for generating a third voltage signal (Ha) proportional to the rotary speed of said motor in operation;   circuit means responsive to said first voltage signal and either said second or third voltage signals for generating voltage signals proportional to S-H or S-Ha;   means for switching the second voltage signal or the third voltage signal to said circuit means;   indicator means responsive to the output of said circuit means; and   means operative when the first voltage signal and the second voltage signal are applied to said circuit means for adjusting the full scale indication of said indicator means, said switching means thereafter enabling the application of the third voltage signal to said circuit means so that said indicator means indicates S-Ha.   
     
     
       2. An apparatus according to claim 1, wherein said circuit means comprises: a differential amplifier.   
     
     
       3. An apparatus according to claim 2, further comprising: means responsive to said third voltage signal for generating an over-scale signal for the protection of said indicator means.   
     
     
       4. An apparatus according to claim 3, wherein said switching means comprises: an automatic switching circuit responsive to said third voltage signal for switching the input of said differential amplifier between said second and third voltage signals.   
     
     
       5. An apparatus according to claim 1, further comprising: circuit means responsive to said signal proportional to S-Ha for transmitting a signal for the control of other equipment associated with said motor.   
     
     
       6. An apparatus according to claim 1, further comprising: an output terminal responsive to said signal proportional to S-Ha for connection to an external indicator.   
     
     
       7. An apparatus according to claim 1, further comprising: a digital meter responsive to said circuit means.   
     
     
       8. An apparatus according to claim 1, wherein said third voltage signal generating means comprises: an AC generator.   
     
     
       9. An apparatus according to claim 1, wherein said third voltage signal generating means comprises: a DC generator.